This invention relates to the drive of a sheet conveyor which is connected to a machine adapted for processing sheets of paper, film, fabrics, metals or the like. The arrangement includes a planetary gear train having a uniform drive and a non-uniform drive, the former being connected to internal gearing of the gear train, and the latter being connected to a cross-bar or crank lever which is operated by the uniform drive. The output of the non-uniform drive is connected to the sheet conveyor for picking up and decelerating the sheets to be discharged.
A sheet conveyor of this general type is disclosed in West German Pat. No. 400,477 wherein sheets of paper, film, fabrics, metals or the like are conveyed after being processed in one form or another. The sheets are processed by passing them through a printing machine, and the sheets can be produced by printing or stamping a continuous web in the printer and cutting them into individual sheets with a cross-cutter or the like after the printing or stamping process.
During the processing operation, the sheets or webs are conveyed at line speed through the processing machine, e.g., a printer. After the sheets have been processed in the desired manner, e.g., by printing or stamping, they are discharged into a receptacle. When the sheets are so discharged, their edges strike a wall of the receptacle, so that considerable forces are exerted on these edges. Since the line speeds of the processing machines are generally high, the edges of the sheets are likely to be unduly damaged if the sheets are discharged at full line speed of a machine such as a printer or a cross-cutter. Therefore, several sheets are normally collected on a collection drum after the processing operation, and are then conveyed onto a moving chain. One or more grippers or the like are attached to this chain for seizing the sheets and holding them during the conveying process until they have arrived at a take-off point. The chains, in turn, are driven by a variable speed drive, which enables them to take off a package of several sheets at the line speed of the collecting cylinder whereafter the conveyed sheets are decelerated to one-fifth the line speed, if five sheets have been accumulated, so that they may be subsequently deposited at a reduced speed into the container or receptacle. The chain, including the grippers attached thereto is again accelerated for taking up the next package of sheets from the collecting drum. Because of the variable speed operation of the chain and of the grippers attached thereto and of the chain-positioning equipment, etc., relatively large masses must be accelerated and decelerated during movement of the chain conveyors. This results in rather substantial inertia forces which, as can be appreciated, influence the drive of the sheet conveyor. For reasons of economy, such drive is normally mechanically connected to the drive provided for the remainder of the machine, for example the drive for the printer or the cross-cutter. Thus, because of the variable speed operation of the conveyor, variable inertia forces are generated which influence the drive of the entire machine, which thereby oftentimes adversely affect the operation of the processing machine upstream of the conveyor and thus impair the quality of the products.
As a solution, it is conceivable to provide separate drives for the processing machines and for the conveyor. However, because of the operating sequence required for the entire installation, the two drives would need to be carefully synchronized with one another. Such synchronization could be accomplished by electrical or electronic means, although this has proven less desireable from a cost standpoint as compared to a mechanical coupling.
Compensation for variable inertia forces through a push-pull modulation of corresponding flywheel masses is disclosed in West German Pat. No. 26 57 861, and U.S. Pat. Nos. 2,211,418 and 2,861,635. However, the drives as therein disclosed take up a great deal of space, so that they are quite unsuitable for a sheet conveying and discharge system. The drive disclosed in U.S. Pat. No. 4,260,144, which is provided with a particular crank gear to meet the requirements for the conveyor drum in a folder, also requires so much space that it cannot be effectively used as the drive for a sheet conveyor.